The present invention relates to a device for monitoring the periodicity of the messages sent over a multiplexed data-transmission network, in particular of a motor vehicle, and especially on a network of the CAN type.
It applies to any monitoring system based on a microcontroller and a bus network controller, in particular of the CAN type, requiring the supervision of the messages sent over the network with an application-specific periodicity.
When data are transmitted periodically on a network of the CAN type, all the controllers which are connected to this network and use the messages containing these data must make sure that the messages have actually been transmitted in a time window allocated by the application in question.
If a message has not been received at the end of a period assigned to it, this may indicate that the controller tasked with transmitting this message is faulty. The controller using these data should be informed of this as soon as possible in order to avoid the use of obsolete data.
At present, the supervision of the periodicity of the messages is entirely undertaken by the microcontroller. This is not generally a problem when the number of messages is small.
When the number of messages becomes large, and these messages have a different and uncorrelated periodicity, the task of the microcontroller becomes too great for the application to be processed correctly.
The object of the invention is to create a device for monitoring the periodicity of the messages sent over a network of the CAN type, which frees the microcontroller from systematically supervising the messages transmitted periodically on the CAN-type network.
It therefore relates to a device for monitoring the periodicity of the messages sent over a multiplexed data-transmission network, in particular of a motor vehicle, characterized in that it includes a memory for storing object messages which are received from the network and each have a value indicating the reception deadline of the message, local clock means which are synchronized by a periodic internal signal and continuously generate a local time-value signal, means for comparing each message-reception deadline value with the local time value and for generating an overdue signal when the value indicating the reception deadline of the message is less than or equal to the local time value, and means for generating a signal, intended for an external microcontroller and indicating that the message has not been received, on the basis of the overdue time signal.